Effects of Combining Feed Grade Urea and a Slow-release Urea Product on Characteristics of Digestion, Microbial Protein Synthesis and Digestible Energy in Steers Fed Diets with Different Starch:ADF Ratios

Abstract

As a result of the cost of grains, the replacement of grains by co-products (i.e. DDGS) in feedlot diets is a common practice. This change produces diets that contain a lower amount of starch and greater amount of fibre. Hypothetically, combining feed grade urea (U) with slow release urea (Optigen) in this type of diet should elicit a better synchrony between starch (high-rate of digestion) and fibre (low-rate of digestion) promoting a better microbial protein synthesis and ruminal digestion with increasing the digestible energy of the diet. Four cannulated Holstein steers (213±4 kg) were used in a 4×4 Latin square design to examine the combination of Optigen and U in a finishing diet containing different starch:acid detergent fibre ratios (S:F) on the characteristics of digestive function. Three S:F ratios (3.0, 4.5, and 6.0) were tested using a combination of U (0.80%) and Optigen (1.0%). Additionally, a treatment of 4.5 S:F ratio with urea (0.80% in ration) as the sole source of non-protein nitrogen was used to compare the effect of urea combination at same S:F ratio. The S:F ratio of the diet was manipulated by replacing the corn grain by dried distillers grain with solubles and roughage. Urea combination did not affect ruminal pH. The S:F ratio did not affect ruminal pH at 0 and 2 h post-feeding but, at 4 and 6 h, the ruminal pH decreased as the S:F ratio increased (linear, p<0.05). Ruminal digestion of OM, starch and feed N were not affected by urea combination or S:F ratio. The urea combination did not affect ADF ruminal digestion. ADF ruminal digestion decreased linearly (p = 0.02) as the S:F ratio increased. Compared to the urea treatment (p<0.05) and within the urea combination treatment (quadratic, p<0.01), the flow of microbial nitrogen (MN) to the small intestine and ruminal microbial efficiency were greater for the urea combination at a S:F ratio of 4.5. Irrespective of the S:F ratio, the urea combination improved (2.8%, p = 0.02) postruminal N digestion. As S:F ratio increased, OM digestion increased, but ADF total tract digestion decreased. The combination of urea at 4.5 S:F improved (2%, p = 0.04) the digestible energy (DE) more than expected. Combining urea and Optigen resulted in positive effects on the MN flow and DE of the diet, but apparently these advantages are observed only when there is a certain proportion of starch:ADF in the diet.

Effects of a combining feed grade urea and a slow-release product on performance, dietary energetics and carcass characteristics of steers fed finishing diets

“…This corroborates the findings of López-Soto et al (2014), which reported an energetic advantage (increases in digestible energy) in cannulated steers when the combination of SRU + U was given at a ratio of starch and ADF identical to that used in the present experiment. In practical terms, if we consider that the diet composition of combined U treatment (SRU + U-4.5) and U treatment at the same S:ADF ratio (U-4.5, Table 1) were practically identical, the energy improvement observed for SRU + U-4.5 treatment represents the equivalent of an increase of 6.4% [(2.14 − 2.00)/2.18] of steam-flaked sorghum in the diet.…”

“…The treatment 1 (SRU) consisted in combining U and SRU product (Optigen II; a polymer-coated urea, Optigen, Alltech Mexico, Guadalajara, Jalisco). Accordingly to the results obtained by López-Soto et al (2014), the U combination used was at 0.80% of each one on DM basis and supplemented in a diet with 4.5 S:ADF ratio. The treatments 2, 3 and 4 were formulated by the supplementation of 0.80% of U solely in diets with 3.5, 4.5 or 5.5 S:ADF ratio.…”

“…Cattle were weighed at the start of experiment, at day 35 and before the steers were harvested (day 73). Based that the better responses on microbial duodenal flows and digestible energy of diet was observed only when U and SRU was combined at same proportion (0.80% of each) in diets which proportion of S:ADF is about 4.5 (López-Soto et al 2014) and that previous reports (Milton et al 1997;Zinn et al 2003) have shown that supplemental U has more positive effects on growth performance or dietary energy utilization when the diet contains a ADF ratio of greater than 5.0, thus, to test our hypothesis, four treatments were formulated as follows. The treatment 1 (SRU) consisted in combining U and SRU product (Optigen II; a polymer-coated urea, Optigen, Alltech Mexico, Guadalajara, Jalisco).…”

“…Changes in the productivity and/or energy efficiency of cattle that have been fed diets containing SRU can be explained by improvements in N retention by decreases in ruminal ammonia concentration and increases in microbial flow to the duodenum (Akay et al 2004;Alvarez-Almora et al 2012). López-Soto et al (2014) showed that steers fed a combination of U and SRU (Optigen) in a diet with a S:ADF ratio of 4.5 had higher (P = 0.04) flows of microbial N and digestible energy of diet than those fed U and those fed U plus SRU in diets with a S:ADF ratio of 3 or 6. They explained that the combination of feed grade U with SRU in diets containing a certain ratio of starch:fibre should promote a better synchrony between starch (high rate of digestion) and fibre (low rate of digestion).…”

“…Hypothetically, combining feed grade U with slowrelease urea (SRU) in this type of diet should elicit a better synchrony between starch (high rate of digestion) and fibre (low rate of digestion). Recent findings (López-Soto et al 2014) indicate that the combination of U and SRU when there is a certain proportion (4.5 to 1) of S: ADF in the diet results in greater improvements in the microbial nitrogen flow and digestible energy of the diet. Because no information is available related to the growth performance and dietary energetics of finishing cattle to verify the findings of López-Soto et al (2014), the aim of this experiment was to examine the effects of the supplementation of U and SRU in a diet with a S:ADF ratio of 4.5 vs. U supplementation in diets with different S:ADF ratios (3.5, 4.5 and 5.5) on growth performance, dietary energetics and carcass characteristics.…”